Struggle with 1st person dialogue
Question: I am trying to write a story with a two person protagonist using a present tense 1st person narrative. I am struggling to write my story in 1st person narrative without always using the word "I." I am trying to work on my 1st person dialogue which is mostly between to teenage girls. Answer:
By "a two person protagonist" I assume you mean two main characters?
As for your questions...
If you are writing in first person, you are going to use the word "I" a lot. Or more precisely, your main character is going to refer to herself as "I" (unless she is one of those strange people who uses her first name in place of the word "I" which can get annoying, to be honest, but might work if she is supposed to be an odd person). At any rate, don't worry about using "I" too much as long as you are using it in a natural way that reflects how that character would tell her story.
In dialogue, it is also perfectly natural for each character to refer to herself as "I." When necessary, your narrator should make it clear to the reader who is speaking.
You do need to be careful about who your narrator is. Regardless of direct speech (which appears within quotation marks), only one character should narrate a scene. Don't switch narrators in the middle of a scene.
If you want to switch between two narrators, make sure there is a distinct break in the text (e.g. a chapter break) so the reader knows a shift in the narration has happened.
Best of luck.